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Best practices for multi-sample variant calling with DeepVariant (WES trio demonstration)

Overview

This document outlines all the steps and considerations for calling and merging a trio using DeepVariant and GLnexus. These best practices were developed and evaluated as described in the article published in Bioinformatics: Accurate, scalable cohort variant calls using DeepVariant and GLnexus (2021).

The process involves 3 major stages: running DeepVariant to create individual genome call sets, running GLnexus to merge call sets, and analyzing the merged call set.

NOTE: This case study demonstrates an example of how to run DeepVariant end-to-end on one machine. The steps below were done on a machine with this example command to start a machine.

The steps in this document can be extended to merge larger cohorts as well.

See this workflow:

workflow

A few things to note before we start:

  • It is recommended to use BAM files with original quality scores. In the case that BAM files went through recalibration, optional DV flags can be used in order to use original scores: --parse_sam_aux_fields, --use_original_quality_scores.
  • DeepVariant optionally allows gVCF output. This option is required for further GLnexus analysis in this document.

Dataset

The Whole Exome Sequencing (WES) dataset we're using is from:

ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/

  • HG002_NA24385_son
  • HG003_NA24149_father
  • HG004_NA24143_mother

Commands for downloading the input BAMs

Just for convenience, we use aria2 to download our data. You can change it to whatever other tools (wget, curl) that you prefer.

To install aria2, you can run: sudo apt-get -y install aria2

DIR="${PWD}/trio"
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG002_NA24385_son/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG002-EEogPU_v02-KIT-Av5_AGATGTAC_L008.posiSrt.markDup.bam -o HG002.bam
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG002_NA24385_son/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG002-EEogPU_v02-KIT-Av5_AGATGTAC_L008.posiSrt.markDup.bai -o HG002.bai
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG003_NA24149_father/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG003-EEogPU_v02-KIT-Av5_TCTTCACA_L008.posiSrt.markDup.bam -o HG003.bam
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG003_NA24149_father/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG003-EEogPU_v02-KIT-Av5_TCTTCACA_L008.posiSrt.markDup.bai -o HG003.bai
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG004_NA24143_mother/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG004-EEogPU_v02-KIT-Av5_CCGAAGTA_L008.posiSrt.markDup.bam -o HG004.bam
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/data/AshkenazimTrio/HG004_NA24143_mother/OsloUniversityHospital_Exome/151002_7001448_0359_AC7F6GANXX_Sample_HG004-EEogPU_v02-KIT-Av5_CCGAAGTA_L008.posiSrt.markDup.bai -o HG004.bai

Command for downloading the reference file

aria2c -c -x10 -s10 -d "${DIR}" https://storage.googleapis.com/deepvariant/exome-case-study-testdata/hs37d5.fa.gz
gunzip ${DIR}/hs37d5.fa.gz
aria2c -c -x10 -s10 -d "${DIR}" https://storage.googleapis.com/deepvariant/exome-case-study-testdata/hs37d5.fa.fai

Command for downloading the input capture region BED file

aria2c -c -x10 -s10 -d "${DIR}" https://storage.googleapis.com/deepvariant/exome-case-study-testdata/agilent_sureselect_human_all_exon_v5_b37_targets.bed

Command for downloading the truth files

HG002:

aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG002_NA24385_son/NISTv4.2.1/GRCh37/HG002_GRCh37_1_22_v4.2.1_benchmark.vcf.gz -o HG002_truth.vcf.gz
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG002_NA24385_son/NISTv4.2.1/GRCh37/HG002_GRCh37_1_22_v4.2.1_benchmark.vcf.gz.tbi -o HG002_truth.vcf.gz.tbi
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG002_NA24385_son/NISTv4.2.1/GRCh37/HG002_GRCh37_1_22_v4.2.1_benchmark_noinconsistent.bed -o HG002_truth.bed

HG003:

aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG003_NA24149_father/NISTv4.2.1/GRCh37/HG003_GRCh37_1_22_v4.2.1_benchmark.vcf.gz -o HG003_truth.vcf.gz
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG003_NA24149_father/NISTv4.2.1/GRCh37/HG003_GRCh37_1_22_v4.2.1_benchmark.vcf.gz.tbi -o HG003_truth.vcf.gz.tbi
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG003_NA24149_father/NISTv4.2.1/GRCh37/HG003_GRCh37_1_22_v4.2.1_benchmark_noinconsistent.bed -o HG003_truth.bed

HG004:

aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG004_NA24143_mother/NISTv4.2.1/GRCh37/HG004_GRCh37_1_22_v4.2.1_benchmark.vcf.gz -o HG004_truth.vcf.gz
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG004_NA24143_mother/NISTv4.2.1/GRCh37/HG004_GRCh37_1_22_v4.2.1_benchmark.vcf.gz.tbi -o HG004_truth.vcf.gz.tbi
aria2c -c -x10 -s10 -d "${DIR}" ftp://ftp-trace.ncbi.nlm.nih.gov/giab/ftp/release/AshkenazimTrio/HG004_NA24143_mother/NISTv4.2.1/GRCh37/HG004_GRCh37_1_22_v4.2.1_benchmark_noinconsistent.bed -o HG004_truth.bed

(No need to install bcftools and other tools, because they are now installed in the DeepVariant images.)

Run DeepVariant on trio to get 3 single sample VCFs

First, install docker if you don't have it yet: sudo apt-get -y install docker.io

With the example command below, it runs DeepVariant on the trio one by one. This is for demonstration only. If you're running this on a large cohort, running serially is not the most effective approach.

N_SHARDS=$(nproc)  # Or change to the number of cores you want to use
CAPTURE_BED=agilent_sureselect_human_all_exon_v5_b37_targets.bed
VERSION=1.6.1

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  BAM=${SAMPLE}.bam

  OUTPUT_VCF=${SAMPLE}.vcf.gz
  OUTPUT_GVCF=${SAMPLE}.g.vcf.gz

  time sudo docker run \
    -v "${DIR}":"/data" \
    google/deepvariant:${VERSION} \
    /opt/deepvariant/bin/run_deepvariant \
    --model_type=WES \
    --ref="/data/hs37d5.fa" \
    --reads="/data/${BAM}" \
    --regions="/data/${CAPTURE_BED}" \
    --output_vcf="/data/${OUTPUT_VCF}" \
    --output_gvcf="/data/${OUTPUT_GVCF}" \
    --num_shards=${N_SHARDS}
done

Note: The BAM files should provide unique names for each sample in their SM header tag, which is usually derived from a command-line flag to the read aligner. If your BAM files don't have unique SM tags (and if it's not feasible to adjust the alignment pipeline), add the --sample_name=XYZ flag to run_deepvariant to override the sample name written into the gVCF file header.

Merge the trio samples using GLnexus

Run GLnexus to merge 3 gVCFs

And then run GLnexus with this config:

sudo docker pull quay.io/mlin/glnexus:v1.2.7

time sudo docker run \
  -v "${DIR}":"/data" \
  quay.io/mlin/glnexus:v1.2.7 \
  /usr/local/bin/glnexus_cli \
  --config DeepVariantWES \
  --bed "/data/${CAPTURE_BED}" \
  /data/HG004.g.vcf.gz /data/HG003.g.vcf.gz /data/HG002.g.vcf.gz \
  | sudo docker run -i google/deepvariant:${VERSION} bcftools view - \
  | sudo docker run -i google/deepvariant:${VERSION} bgzip -c \
  > ${DIR}/deepvariant.cohort.vcf.gz

When we ran on this WES trio, it took only about 13 seconds. For more details on performance, see GLnexus performance guide.

For a WGS cohort, we recommend using --config DeepVariantWGS instead of DeepVariantWES. Another preset DeepVariant_unfiltered is available in glnexus:v1.2.7 or later versions for merging DeepVariant gVCFs with no QC filters or genotype revision (see GitHub issue #326 for a potential use case). The details of these presets can be found here.

Annotate the merged VCF with Mendelian discordance information using RTG Tools

Create an SDF template from our reference file:

sudo docker run \
  -v "${DIR}":"/data" \
  realtimegenomics/rtg-tools format \
  -o /data/hs37d5.sdf /data/hs37d5.fa

Create a PED file $DIR/trio.ped that looks like this (with the sample name of the trio):

FILE="${DIR}/trio.ped"
cat <<EOM >$FILE
#PED format pedigree
#
#fam-id/ind-id/pat-id/mat-id: 0=unknown
#sex: 1=male; 2=female; 0=unknown
#phenotype: -9=missing, 0=missing; 1=unaffected; 2=affected
#
#fam-id ind-id pat-id mat-id sex phen
1 Sample_Diag-excap51-HG002-EEogPU Sample_Diag-excap51-HG003-EEogPU Sample_Diag-excap51-HG004-EEogPU 1 0
1 Sample_Diag-excap51-HG003-EEogPU 0 0 1 0
1 Sample_Diag-excap51-HG004-EEogPU 0 0 2 0
EOM

Annotate merged VCF with RTG Tools

sudo docker run \
  -v "${DIR}":"/data" \
  realtimegenomics/rtg-tools mendelian \
  -i /data/deepvariant.cohort.vcf.gz \
  -o /data/deepvariant.annotated.vcf.gz \
  --pedigree=/data/trio.ped \
  -t /data/hs37d5.sdf \
  | tee ${DIR}/deepvariant.input_rtg_output.txt

The output is:

Checking: /data/deepvariant.cohort.vcf.gz
Family: [Sample_Diag-excap51-HG003-EEogPU + Sample_Diag-excap51-HG004-EEogPU] -> [Sample_Diag-excap51-HG002-EEogPU]
Concordance Sample_Diag-excap51-HG002-EEogPU: F:58162/58675 (99.13%)  M:58574/58690 (99.80%)  F+M:57946/58580 (98.92%)
Sample Sample_Diag-excap51-HG002-EEogPU has less than 99.0 concordance with both parents. Check for incorrect pedigree or sample mislabelling.
828/58912 (1.41%) records did not conform to expected call ploidy
58818/58912 (99.84%) records were variant in at least 1 family member and checked for Mendelian constraints
187/58818 (0.32%) records had indeterminate consistency status due to incomplete calls
644/58818 (1.09%) records contained a violation of Mendelian constraints

From this report, we know that there is a 1.10% Mendelian violation rate, and 0.32% of the records had incomplete calls (with .) so RTG couldn't determine whether there is violation or not.

Single sample quality metrics

In addition to the cohort quality statistics, for completeness we generate single-sample quality metrics.

ti/tv ratio

We run bcftools stats on the 3 VCF outputs. Since our DeepVariant run already constrained to just the capture regions, no need to specify it again here. We had to pass in the -f PASS flag so that only the PASS calls are considered.

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  sudo docker run \
  -v ${DIR}:${DIR} \
  google/deepvariant:${VERSION} \
  bcftools stats -f PASS \
    ${DIR}/${SAMPLE}.vcf.gz \
  > ${DIR}/${SAMPLE}.stats
done

| Sample | [3]ts | [4]tv | [5]ts/tv | [6]ts (1st | [7]tv (1st | [8]ts/tv (1st | : : : : : ALT) : ALT) : ALT) : | ------ | ----- | ----- | -------- | ---------- | ---------- | ------------- | | HG002 | 29934 | 11684 | 2.56 | 29919 | 11665 | 2.56 | | HG003 | 29808 | 11749 | 2.54 | 29795 | 11727 | 2.54 | | HG004 | 30039 | 11850 | 2.53 | 30027 | 11833 | 2.54 |

If you want to restrict to the truth BED files, use this command:

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  sudo docker run \
  -v ${DIR}:${DIR} \
  google/deepvariant:${VERSION} \
  bcftools stats -f PASS \
    -T ${DIR}/${SAMPLE}_truth.bed \
    ${DIR}/${SAMPLE}.vcf.gz \
  > ${DIR}/${SAMPLE}.with_truth_bed.stats
done

Which resulted in this table:

| Sample | [3]ts | [4]tv | [5]ts/tv | [6]ts (1st | [7]tv (1st | [8]ts/tv (1st | : : : : : ALT) : ALT) : ALT) : | ------ | ----- | ----- | -------- | ---------- | ---------- | ------------- | | HG002 | 27704 | 10546 | 2.63 | 27696 | 10533 | 2.63 | | HG003 | 27356 | 10514 | 2.60 | 27351 | 10502 | 2.60 | | HG004 | 27491 | 10604 | 2.59 | 27484 | 10593 | 2.59 |

Rtg vcfstats

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  sudo docker run \
  -v "${DIR}":"/data" \
  realtimegenomics/rtg-tools vcfstats \
  /data/${SAMPLE}.vcf.gz \
  > ${DIR}/${SAMPLE}.vcfstats
done

which shows the following:

HG002:

Location                     : /data/HG002.vcf.gz
Failed Filters               : 14598
Passed Filters               : 45258
SNPs                         : 41584
MNPs                         : 0
Insertions                   : 1867
Deletions                    : 1783
Indels                       : 22
Same as reference            : 2
SNP Transitions/Transversions: 2.56 (41838/16338)
Total Het/Hom ratio          : 1.49 (27087/18169)
SNP Het/Hom ratio            : 1.51 (25017/16567)
MNP Het/Hom ratio            : - (0/0)
Insertion Het/Hom ratio      : 1.08 (969/898)
Deletion Het/Hom ratio       : 1.53 (1079/704)
Indel Het/Hom ratio          : - (22/0)
Insertion/Deletion ratio     : 1.05 (1867/1783)
Indel/SNP+MNP ratio          : 0.09 (3672/41584)

HG003:

Location                     : /data/HG003.vcf.gz
Failed Filters               : 15423
Passed Filters               : 45150
SNPs                         : 41519
MNPs                         : 0
Insertions                   : 1851
Deletions                    : 1752
Indels                       : 21
Same as reference            : 7
SNP Transitions/Transversions: 2.52 (41645/16537)
Total Het/Hom ratio          : 1.48 (26923/18220)
SNP Het/Hom ratio            : 1.50 (24879/16640)
MNP Het/Hom ratio            : - (0/0)
Insertion Het/Hom ratio      : 1.11 (974/877)
Deletion Het/Hom ratio       : 1.49 (1049/703)
Indel Het/Hom ratio          : - (21/0)
Insertion/Deletion ratio     : 1.06 (1851/1752)
Indel/SNP+MNP ratio          : 0.09 (3624/41519)

HG004:

Location                     : /data/HG004.vcf.gz
Failed Filters               : 15166
Passed Filters               : 45515
SNPs                         : 41857
MNPs                         : 0
Insertions                   : 1859
Deletions                    : 1778
Indels                       : 20
Same as reference            : 1
SNP Transitions/Transversions: 2.55 (41671/16373)
Total Het/Hom ratio          : 1.57 (27794/17720)
SNP Het/Hom ratio            : 1.59 (25691/16166)
MNP Het/Hom ratio            : - (0/0)
Insertion Het/Hom ratio      : 1.12 (983/876)
Deletion Het/Hom ratio       : 1.62 (1100/678)
Indel Het/Hom ratio          : - (20/0)
Insertion/Deletion ratio     : 1.05 (1859/1778)
Indel/SNP+MNP ratio          : 0.09 (3657/41857)

Run hap.py to calculate the accuracy of DeepVariant generated call sets

sudo docker pull jmcdani20/hap.py:v0.3.12

declare -a trio=(HG002 HG003 HG004)
for SAMPLE in "${trio[@]}"
do
  sudo docker run -i \
    -v "${DIR}":"/data" \
    jmcdani20/hap.py:v0.3.12 /opt/hap.py/bin/hap.py \
    "/data/${SAMPLE}_truth.vcf.gz" \
    "/data/${SAMPLE}.vcf.gz" \
    -f "/data/${SAMPLE}_truth.bed" \
    -T "/data/${CAPTURE_BED}" \
    -r "/data/hs37d5.fa" \
    -o "/data/${SAMPLE}.happy.output" \
    --engine=vcfeval \
    --pass-only > ${DIR}/${SAMPLE}.stdout
done

Accuracy F1 scores:

Sample Indel SNP
HG002 0.974074 0.993897
HG003 0.972967 0.993939
HG004 0.972967 0.993939